This invention relates to powder metallurgy. More particularly, it relates to a method of producing silicon steel strip by means of powder metallurgy.
It is well known that silicon steel sheet is characterized by electrical properties that render it well suited for fabrication into electrical products such as laminated transformer cores. In the past, silicon steel sheet has been produced by preparing a heat of low carbon steel and adding the desired amount of silicon to the steel either in the molten bath or in the ingot mold into which the heat is poured. The steel is then rolled in several different steps into steel strip of the desired gauge.
Silicon steel strip usually is made to contain from about 0.5 to 6.0% silicon. Steels containing up to about 2.00% silicon can be rolled without undue difficulty. However, steels containing higher amounts of silicon are brittle and difficult to work. Consequently, the production of steel strip containing such higher silicon contents requires heavy mill equipment, small drafts per pass, and frequent annealing between passes. In an effort to obviate these difficulties, efforts have been made to produce silicon sheet by powder metallurgy. For example, low carbon steel strip was first coated with a liquid, e.g., tridecyl alcohol, onto which a silicon-containing powder was supplied by means of brushes rotating in a bed of dry powder positioned beneath the strip. The powder was then compacted onto the strip by rolling. Next, the powder was diffused throughout the strip by means of a heat treatment. Finally, this strip was given a light rolling, to obtain the desired gauge, and heat treated to develop the desired magnetic properties.
Strip produced by this powder metallurgical process was characterized by a nonuniform silicon content because of an inability to provide a uniformly thick coating of powder on the strip surface. In addition, the diffusion time was unduly long.
It is an object of the present invention to provide a method by which an electrical steel sheet having a uniform silicon content is produced. Furthermore, the diffusion treatment time is to be minimum.
It is a further object of this invention to provide a method for producing a product in which an element "m" is uniformly diffused throughout a substrate in a minimum time.